Boiled alive

The 2003 heatwave killed more than 30,000 people. It was the biggest natural disaster in Europe on record, according to the government's chief scientific adviser. And yet, as temperatures reach new highs, Britain is fretting about dried-out lawns and stuffy offices. Alok Jha looks at the dangers that really lie ahead - and how to survive them

When the human body gets to 42C, it starts to cook. The heat causes the proteins in each cell to irreversibly change, like an egg white as it boils. Even before that, the brain shuts down because of a lack of blood coming from the overworked, overheated heart. Muscles stop working, the stomach cramps and the mind becomes delirious. Death is inevitable.

The gruesome effects of overheating have been largely forgotten as Europe swelters under record temperatures, from southern England's 36.5C to Bosnia's 41C. When weather forecasters predicted that the heat would get more intense across the continent today, most of us heaved a sigh at the thoughts of stuffy trains, sweaty buses, parched lawns and boiling offices. But perhaps we are being complacent.

Already, people across Europe are succumbing to the heat. In France, at least 40 people, mostly elderly, have already died. The latest reported victim was a 90-year-old woman found dead in Orly, near Paris - her body temperature had reached 41C. In Spain, six people have died so far. In Germany and Holland, two people have died from heat-related injuries.

Last weekend in Britain, 87-year-old Don Goodheart, a veteran of the second world war, died while on standard-bearing duty outside a church in Devon. He suffered a heart attack while standing under the blazing sun.

Heatwaves claim thousands of lives, killing more people each year than floods, tornadoes and hurricanes combined. And it is going to get worse. Scientists calculate that, as global warming bites and average temperatures around the world get higher, the risk of extreme heatwaves will also increase. The World Meteorological Organisation estimates that the number of heat-related deaths across the globe will double in the next 20 years.

To see these statistics in action, think back three years. In 2003, Europe was melting. It was the hottest summer ever recorded in the northern hemisphere and temperatures were consistently soaring to more than 40C across many parts of the continent. Britain recorded its first ever temperature of more than 100F on August 10.

The surprise at the heat was matched only by shock at the scale of the human casualties it caused: more than 2,000 people died in Britain, 7,000 in Germany, 4,000 in Spain and 1,000 in Italy. The largest casualties were in France, where almost 15,000 perished in the first three weeks of August, more than 19 times the global death toll from the Sars epidemic earlier that year.

The UK government's chief scientific adviser, Sir David King, says that the 2003 heatwave was "the biggest natural disaster in Europe on record. Thirty-two thousand fatalities makes it an enormous natural disaster." According to Janet Larsen of the Earth Policy Institute (EPI), a Washington DC-based thinktank, the 2003 heatwave in Europe was "the greatest such event the world has ever seen".

If the summer of 2003 had been a freak occurrence, northern Europeans may have been able to rest easy. But the latest climate models paint a very bleak picture, suggesting that the summer of 2003 will be the norm in Europe by the 2040s. For those countries that are not well adapted to dealing with excessively high temperatures, the consequences could be catastrophic.

Throughout its life, the human body battles to keep its core temperature at a steady 37C, whatever conditions it finds itself in. This is the temperature at which the organs function normally and there is little tolerance to change. To prevent overheating, the body starts pumping blood to the skin's surface when it senses that things are getting warm. This places extra strain on the heart and, as the water from the blood evaporates, it thickens the blood, leading to an increased risk of clotting - which can cause strokes or heart attacks.

If the core temperature continues to rise, muscles stop working properly because of the amount of water and salts being lost through sweating. Eventually, when the brain reaches 38.5C, the body suffers a heatstroke. If the temperature is not brought down quickly at this stage, death soon follows.

The problems of heat stress on the body get more serious with age. The older a person is, the less efficient their body's temperature regulation. "They are not as sensitive," says James Goodwin, a physiologist and head of research at Help the Aged. "An older person won't notice the cold as soon as a younger person does and that's a problem because they won't respond to it quite so quickly. In the heat, they don't perceive that temperatures are rising so quickly and don't make the behavioural adjustments to cool quite so quickly."

For all the danger, preventing heat deaths is very simple. "There's no reason anyone should die of the hot weather," says Sari Kovats, a researcher on the health implications of heatwaves at the London School of Hygiene and Tropical Medicine. "As long as the person's cool and given water and salts so they can sweat. It's very simple but you need some sort of active care."

The 2003 heatwave showed how ill-prepared European countries were for the onslaught of high temperatures. Public health officials did not use weather forecasts to predict possible emergencies and there was no concept that a summer of high temperatures would be such a major problem. In France, large numbers of medical staff were off on holiday all at once - the health service there did not foresee any problem. "The notable feature of the French episode was the health minister appearing on the TV and saying, 'Crisis, what crisis?'," says Godwin. "He wasn't being disingenuous - he hadn't got the data."

There were no real-time surveillance systems in place to assess how many people were being admitted to hospitals and how many of them were dying of the heat. Andrew Haines, director of the London School of Hygiene and Tropical Medicine, says that those problems were exacerbated by people's unfamiliarity in living with high temperatures. "In Paris, where there's not a lot of air-conditioning, many of the people that died were in residential homes or they were in the top floors of houses where heat gets trapped. People couldn't cool down overnight." King agrees: "That's the problem in France - none of the people had ever experienced anything like this before."

The prospect of even hotter summers in the decades to come - an inevitable result of climate change - will mean that northern Europeans will need to change the way they behave sooner rather than later.

Human-induced climate change - caused by the emission of greenhouse gases into the atmosphere - loomed large as a possible explanation for the 2003 heatwave in the months that followed. A simple connection is too simplistic - no extreme weather event can be tied directly to climate change because it might have occurred by chance in an unchanged climate. But it is possible to work out how much human activity has increased the risk that extreme weather events - such as heatwaves - will occur.

Peter Stott, a climate scientist at the Hadley Centre for Climate Prediction and Research in Exeter, looked at how the chances of getting a hot summer had changed as a result of greenhouse gas emissions and other human influences. "We did that by comparing climate models simulations with the observed record," says Stott. "We had climate change models that included greenhouse gas emissions and then other simulations that didn't. By comparing the two, we could look at what the risk of having a very hot summer is now and compare that to what the risk could have been if there hadn't been any human-influenced climate change."

His model, published in the science journal Nature, showed that human influences had at least doubled the chance of summers as hot as the one Europe saw in 2003. In a normal climate, the chance of getting a summer as hot as 2003 would have been around once every millennium. In Stott's climate models, greenhouse gas emissions had contributed to an increase in 2003-style summers to at least once in every 500 years and possibly as high as once in every 250 years.

"The problem is that we've got a baseline increase in average summer temperature, and that arises from the global warming that is happening right now," says King. "If you take the average summer temperature in central Europe today, it's roughly 0.6C higher than it was in the middle of the last century. This means that if you have a heatwave, where the temperature might be 0.5 to 1C above average, it's now sitting on top of a higher figure. The impact is going to be all the greater."

"According to the model predictions, by the 2040s, the 2003-type summers will be happening every year," says Stott.

The climate models are unequivocal in their pessimism for the future. But the notion that extreme heat will become a fact of life for Europeans does not necessarily imply an unchecked increase in related deaths. King says northern Europeans can learn a lesson or two from their neighbours to the south. "If you go to a country where people are used to the heat - if you go to Greece, say - the Brits are all out lying in the sun, the Greeks are sitting in the shade. The Greeks will leave their houses with all their shutters closed so the sun doesn't go in through the windows. They will run grapevines on the outside of their houses so the walls are shaded. It's all a matter of adapting to a hotter climate," he says.

Educating people most at risk - those working outside, the elderly and children - as to how to stay cool, drink enough and stay indoors at the hottest part of the day is important. But people also need to think about the entire course of a heatwave, which may last several days.

"If people don't get a cooling opportunity, it means that people don't have a chance to lower their temperature properly," says Goodwin. "It leads to maintained sweating throughout the night, loss of sodium and the increased risk of a heart attack or a stroke."

Robert Jones, head of the minor injuries unit at Gravesham Community Hospital in Kent, says that the elderly in particular may not take the opportunity to cool down at night by opening windows. "The problem in the community is that the elderly who live on their own on ground floors are frightened to open the windows because of vandalism and burglary," he says. "[The nurses] have to open the windows when they go in because it's stifling."

The UK government developed its first heatwave warning system in 2004, in the wake of the previous summer's deaths. Officials in the Department of Health and the National Health Service are also working with the Met Office in trying to produce a regular health forecast. "If we can forecast the weather, and we know weather affects health, we can forecast how people's health will change over the next 10 days. We can therefore take action to prevent health getting worse," says Goodwin.

On the awareness front, Jones says that hospitals such as his are successfully spreading the word to the most vulnerable groups on how to be sensible in hot weather. "We've got cold fluids to offer them, we've bought fans, we're opening windows. So they can see what we're doing."

In the longer term, northern European countries will have to start building some of the problems posed by high temperatures and climate change out of their cities. "The issue for the UK is all about the housing. None of the housing is taking climate change into account," says Kovats. Most of the UK lives in a built environment designed by the Victorians. By providing clean water into every home and pumping sewage out, the Victorians dealt with the problems of water-borne diseases, but the homes they built are energy inefficient and entirely unsuited as refuges in the event of extreme heat. Air conditioning can help but, in the end, only contributes to the greenhouse effect by burning fossil fuels.

This is an issue that King is already thinking about. He is tinkering with the idea of setting up a government-backed project that will map out a better way to design buildings for the future. "There are ways of doing passive air conditioning that don't use energy, and you can build that into design," he says. "You can introduce something called a thermal chimney to a building, which is simply using the heat at the top of the house, and the fact that hot air is less dense and rises, to pull cold air from a basement area where you've got a cold water tank."

Warmer countries could also provide inspiration for much simpler ideas. "You have external shutters so that you reflect heat away from the window pane," says King. "We don't have external shutters in general. We want the heat in. Once the heat is through the window, and in the room, having blinds inside is useless." These ideas are important, but they will come at a cost, given the number of houses across Europe that will need upgrading.

Heat stress and the effects of hyperthermia are certain to become more common as the world heats up over the next century. But Goodwin says that no one is served by a general panic. "You've got to understand the risks and change how you live slightly to cope with those risks. The issue is to say to people not to work in fear on this but to realise they can, by fairly conservative means, reduce the risks".

How to prevent heatstroke

· Shade south-facing windows and stay in during the hottest part of the day (11am-3pm)

· Ensure rooms are well-ventilated

· Drink plenty of water or fruit juice, even if you are not thirsty

· Avoid alcohol, tea or coffee as these can lead to further dehydration

· Wear light, loose-fitting clothing

· Take regular showers to cool down

· Eat cold foods such as salads or fruit as they have a high water content

· Look in on elderly relatives or neighbours, particularly if they are living alone

How to spot it

· Symptoms of heat exhaustion include cramp in the arms, legs or stomach, feelings of mild confusion, weakness or problems sleeping

· The more serious heatstroke is a collapse in the body's functions, marked by dry skin, a rapid heart rate, delirium and, eventually, unconsciousness

· Those at most risk include older people (especially those over 75), people suffering from mental ill-health or dementia, those who are bed-bound and people on certain medications such as beta blockers or anti-hypertension drugs

How to treat it

· Cool people down gently with tepid water. Do not throw cold water on a person with heatstroke - it makes the body think it is losing heat, so it shuts down the circulation to the skin. That means all the hot blood in the skin is diverted inwards to the brain

· Lift their feet to allow blood to flow back to the heart and brain

· Apply a cold compress to face and neck

· Avoid giving drugs such as aspirin

French lessons

France was on alert yesterday as temperatures soared to 38C - just over 100F - in parts of the country. The current heatwave has already killed at least 40 people, among them a 90-year-old in an old people's home, a 45-year-old man suffering from schizophrenia who was found wearing nine layers of clothing, and an 81-year-old man who was found dead at his flat in eastern France.

But that's nothing compared with August 2003, when around 15,000 fell victim to the "canicule". Most were elderly; many had been left to fend for themselves as their families disappeared for the annual holidays without so much as a phone call to check mamie and papy - gran and grandad - were bearing up as temperatures rose to over 40C (104F).

The death toll was worst in old peoples' homes and (less surprisingly) in stifling cities where the old, friendless and abandoned succumbed to the heat in anonymous apartments. Dozens of relatives returned to Paris to discover the bodies of their loved ones were being stored in a refrigerated warehouse, normally used for frozen vegetables, on the city's outskirts.

Many doctors and nurses and most of the government were also on holiday - and stayed there. Officials, including President Jacques Chirac, who failed to return as the crisis worsened, were accused of being part of the collective selfishness. The fact that it took several weeks to identify many of the victims, some of whom were never claimed and were buried in unmarked graves, added to a sense of national shame.

"Despite the many criticisms of the NHS, it is unlikely this would have happened in the UK because most doctors' surgeries have lists of the elderly people on their books and would check up on them," said one British doctor working in Paris. "France doesn't have strong primary health care like district nurses, health visitors, community paediatricians, social workers ... ie, a team of people who can keep tabs on the health of those in the community."

"Solidarity does not go on holiday" is the French government's catchphrase this summer as it bombards the public with advice and information on how to combat the heat: drink 1.5 litres of water a day, spend two hours in an air-conditioned room, close the shutters, run your forearms under water ...

Kim Wilsher

Meanwhile in the rest of the world ...

United States Temperature hits 48.8C in South Dakota, 46C in California. Hundreds of thousands are left without power as air-conditioners overload the electricity grid. At least 10 suspected heat-related deaths are reported.

Canada Temperature tops 34C in Toronto. Extreme health alert issued; city officials believe there is a 90% chance of heat-related deaths. Municipal swimming pools are kept open late into the night.

France Temperature tops 38C in Bordeaux and 39C in Paris. France's main electricity provider has to buy power from abroad as the national grid strains in the heat. Production curtailed at nuclear power plants because of a shortage of cold water used in cooling. Four giant humidifiers are placed at the foot of the Eiffel Tower to spray water vapour on passersby. At least 40 believed dead, including a 15-month-old baby.

Germany Temperature reaches 39C in Berlin. The Unterweser nuclear plant reduces output by 30% due to a lack of cold water. Two deaths due to suspected heat-related causes.

Spain Temperature reaches 40C. Two new victims of the heatwave reported last week, including a Barcelona sunbather and a man working in a greenhouse on the south coast. Six dead from the heatwave so far.

Netherlands Temperature tops 37C. A four-day walking event is cancelled in Nijmegen after two participants die in the heat and 30 are hospitalised.

Poland Temperatures up to 35C. Members of the ruling Conservative party prepare to pray for rain.

Czech Republic Temperature over 35C in Prague. The famous medieval clock in the centre of the city is running slow because of the heat, officials announce.

Denmark Temperature hits 33.5C. Police report a spate of thefts, prompted by house owners leaving doors and windows open to cope with the heat. There is an increase in complaints about public sex on beaches.

Austria Temperature reaches 36C. Barbecues are banned from public areas to prevent forest fires. A German truck driver dies from heat-related causes.

Italy Temperature reaches 39C in Florence.

Italy's largest river, the Po, shrinks to its lowest level since records began. Emergency workers in Rome hand out water to people standing in queues outside museums and galleries or waiting in the sun to catch their bus. One worker in Sardinia collapses and dies of heat-related causes.

Bosnia Temperature reaches 41C. A series of fires break out, prompting firefighters to ask the army for helicopter assistance.